A number of new protocols were introduced to examine brain aging and cerebral metabolism. In using the isotope fluoro-18-deoxyglucose with positron emission tomography, we found that cerebral glucose utilization does not change with advancing age in healthy males, but changes are found in patients with Alzheimer's disease and Down syndrome. Three new protocols allow us to evaluate these findings and determine their specificity. Studies are underway in multiinfarct dementia, the second leading cause of dementia; a major depressive disorder both with and without cognitive impairment; and fragile-X syndrome to evaluate PET alterations uncovered in our laboratory in subjects with Down syndrome. The role-of the dopaminergic system in normal aging, Alzheimer's disease with and without extrapyramidal signs, and familial inverted chorea will be explored with 6-[18-F]-fluoro-L-Dopa (6-FD) and positron emission tomography (PET).